Post Prelim 3 and Final – Flashcards
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| ways to synthesize ethers |
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| williams alkoxy mercuration/reduction (alcohol dehydration and alkene addition--not talk about in class-require strong acid and heat and 2 primary alcohols-symmetrical ethers, unsym ethers--3', dilute strong acid) |
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| williams |
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| alcohol----- ether alcohol + strong base (with THF) yields strong nuc and primary (or methyl) halide Sn2 to create ether -tertiary, secondary alkyl halides can not be used (formed) |
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| alkoxy mercuration |
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| alkene------ether alkene (alcohol solvent) 1. Hg(OAc) (racemic) 2. NaBH4, HO- form racemic mixture |
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| Ether reactivity |
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| stable to strong bases and nuc reactive to strong acids Sn2, Sn1, E1 |
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| Epoxide synthesis |
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| halohydrin cyclization Direct epoxidation |
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| direct epoxidation (alkene oxidation by peracids) |
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| peracid + benzene (any alkene)----epoxide concerted syn addition 5 arrows |
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| Halohydrin cyclization |
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| 1. alkene + Br2 (in H20) 2. Base (H0- or pyridine) ANTI (backside attack) |
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| Epoxide reactivity |
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| 1. Grignard (-MgBr) |
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| Sharpless Asymmetric Epoxidation |
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| (uses +OOH, Ti (cat)) yield extremely selective eposide |
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| Glycol Synthesis |
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| 1. epoxide hydrolysis 2. osmylation of alkenes 3. catalytic osmylation |
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| epoxide hydrolysis |
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| epoxide +H2O, H+ yield racemic glycol |
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| osmylation of alkenes |
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| OsO4 + alkene---osmate ester--)+H20---glycol (+detox) concerted syn addition |
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| catalytic osmylation |
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| alkene + OsO4 + TMAO in pyrimidine and H20---glycol |
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| glycol cleavage rxn oxidation |
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| Glycol + H5IO6---intermediate cyclic per-iodate ester----aldehydes and ketones |
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| nuc sub of epoxides under BASIC conditions |
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| 1. nuc sub 2. proton transfer unsymmetric epoxides nuc react at least sub alkyl groups inversion of config |
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| nuc sub of epoxides under ACIDIC conditions |
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| react with most sub alkyl group of epoxide 3' 2',1' give mixtures inversion of configuration if H20 is used as nuc product is glycol |
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| IR |
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| stretching and bending of bonds |
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| E= |
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| hv=(hc)/lambda |
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| transmittance |
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| emmergent/incident light I/I0 |
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| 3 principles of IR |
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| 1. bond stretching costs more E than bonding (higher f) 2. longer bonds (to heavier atoms) vibrate more easily than shorter bonds (to lighter atoms) (lower f) 3. single bonds vibrate more easily than multiple bonds (lower f) |
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| IR limits |
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| must be a change in dipole moment symmetrical not see IR |
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| Region 3600 cm-1 - 1600 cm-1 (left side of IR) |
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| highest E most stretching diagnostic characteristic |
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| 1600cm-1- 600 cm-1 (right side of IR) |
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| fingerprint region |
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| electron impact ms |
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| mw m---m+ (parent ion) use m/z for mw----fragmentation---- ch3+---ch2+ |
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| CIMS |
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| gentler technique M+ CH4+---H+----[M-H]+ = CH3 radical |
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| for a compound having n carbons in ms |
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| n= (m+1)/m/(1.1) |
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| if odd number of N atoms, molecular weight will be |
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| odd |
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| electrospray ionization |
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| genetle all parent ions present spray mist of droplets, evap, gas phase ions |
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| ms frag patterns: alkenes |
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| parent ion even frag odd |
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| ms frag patterns: ethers |
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| inductive cleavage, 2 pathways |
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| ms frag patterns: alcohols and ethers: alpha cleavage |
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| frag odd mass (even m/z m+) |
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| ms frag patterns: primary alcohol 2 bond fragmentation |
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| exception even m+, EVEN mass fragment |
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| NMR |
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| nuc spin states HextXhX gyromagnetic ratio hv = resonant frequency |
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| Hnet= |
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| Hext + Hinduced + Hnearby nuc Hnet<Hext |
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| chemical shift Si (in ppm)= |
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| (vi-vtms)/vinstrument |
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| homotopic h |
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| always same chem shift |
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| enantiopopic h |
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| same chem shift in achiral/racemic medium but may be different in chiral medium |
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| diast h |
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| may have different chem shifts in any medium |
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| shielding |
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| decreased local mag field by circulation of nearby e- decreased e-neg--increased shielding magnetic field of less shielded higher |
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| As increase ppm |
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| increase local field at protons decrease shielding protons increase proton chem shift |
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| increase in chem shift due to (3) |
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| increased e-neg increased # e-neg groups decreased distance of e-neg groups |
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| when change in chemical shift is greater than J (constant) |
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| n adjacent H give rise to n+1 multiplet relative intensities are predicted by pascals triangle |
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| J magnitude |
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| Highest with H on same carbon (10-20 Hz) and if double bond-trans |
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| NMR can not detect... |
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| alcohol, too rapid chem equil |
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| 13C NMR |
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| fourier transform technique -excite all 13C at once -collect data (intensities over time) -can transform data into intensities vs frequency -Bc integrated peak areas are unreliable -13C has a broad chem shift range -watch for symmetry |
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| alkynes |
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| two pi bonds good lewis bases |
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| addition rxns alkynes |
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| HBR H20 Hydroboration oxidation rxn |
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| addition rxns alkynes |
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| HBR H20 Hydroboration oxidation rxn |
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| HBR + alkyne |
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| 2 -Br groups |
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| H20 addition |
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| with Hg+1, H2SO4 enol- ketone acid (2 steps) base (1 step) |
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| If unsymmetric alkynes |
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| give mixture of ketones H20, hydroboration |
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| Hydroboration oxidation of alkynes |
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| disamyl borane concerted cyn additon antimarkovinikov enol--- aldeyhyde |
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| alkyne reduction reactions |
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| 1. hydrogenation 2. lindars 3. Na metal in liquid NH3 reduction |
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| alkyne hydrogenation |
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| goes all the way to alkane unless poisoned by Pb(OAc)2 and with CaCO3 (lindlars) to create CIS alkene only |
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| Na Metal in liquid NH3 reduction of an akyne |
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| yield TRANS alkene |
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| Substitution reaction of alkynes |
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| Need strong base NaNH2, LDA, R-MgX electrophiles: alkyl halide toluide good for extending C networds |
